U.S. patent application number 12/456427 was filed with the patent office on 2010-04-08 for system and method for drying and torrefaction.
This patent application is currently assigned to Wyssmont Co. Inc.. Invention is credited to Joseph Bevacqua, Robert Borre, Edward Weisselberg.
Application Number | 20100083530 12/456427 |
Document ID | / |
Family ID | 42074629 |
Filed Date | 2010-04-08 |
United States Patent
Application |
20100083530 |
Kind Code |
A1 |
Weisselberg; Edward ; et
al. |
April 8, 2010 |
System and method for drying and torrefaction
Abstract
A method and apparatus for torrefaction of water containing
cellulosic materials is performed in an inert atmosphere. The
cellulosic material is cascaded through the apparatus between a
plurality of rotatable trays vertically stacked within multiple
processing zones. Steam being generated from heating of the
cellulosic material is recycled back to the apparatus to provide an
inert atmosphere. The steam may be superheated in a heat exchanger.
Exhaust from the torrefaction zone of the apparatus has some
moisture and other volatiles removed prior to being reheated in a
burner. The heated exhaust is used in the heat exchanger to
superheat the recycled steam.
Inventors: |
Weisselberg; Edward;
(Kinnelon, NJ) ; Bevacqua; Joseph; (Leonia,
NJ) ; Borre; Robert; (Wurtsboro, NJ) |
Correspondence
Address: |
LERNER, DAVID, LITTENBERG,;KRUMHOLZ & MENTLIK
600 SOUTH AVENUE WEST
WESTFIELD
NJ
07090
US
|
Assignee: |
Wyssmont Co. Inc.
Fort Lee
NJ
|
Family ID: |
42074629 |
Appl. No.: |
12/456427 |
Filed: |
June 15, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61195092 |
Oct 3, 2008 |
|
|
|
Current U.S.
Class: |
34/505 ; 34/169;
34/171; 34/468; 34/516; 34/77 |
Current CPC
Class: |
F26B 17/001 20130101;
Y02E 50/30 20130101; Y02E 50/15 20130101; C10L 5/447 20130101; C10L
9/083 20130101; F26B 23/022 20130101; Y02E 50/10 20130101; Y02E
50/14 20130101 |
Class at
Publication: |
34/505 ; 34/77;
34/169; 34/516; 34/468; 34/171 |
International
Class: |
F26B 3/16 20060101
F26B003/16; F26B 21/00 20060101 F26B021/00; F26B 17/14 20060101
F26B017/14 |
Claims
1. An apparatus for the torrefaction of water-containing cellulosic
material within an inert atmosphere, said apparatus comprising, a
material processing chamber having a plurality of processing zones
adapted for processing water containing cellulosic material, a
plurality of material supports arranged within said processing
zones for receiving cellulosic material cascading within said
chamber, said material processing chamber having a first outlet for
the discharge of steam generated from processing the cellulosic
material within said processing zones, and at least one inlet for
recycling at least a portion of said steam into said material
processing chamber, whereby said steam at least partially provides
an inert atmosphere within said material processing chamber.
2. The apparatus of claim 1, further including a condenser arranged
in fluid communication with said outlet of said material processing
chamber through which said steam passes, said condenser adapted for
removing water from said steam.
3. The apparatus of claim 1, further including a heat exchanger for
heating said steam being recycled to said material processing
chamber.
4. The apparatus of claim 3, wherein said heat exchanger superheats
said steam.
5. The apparatus of claim 1, further including a condenser arranged
in fluid communication with said first outlet of said material
processing chamber through which a first portion of said steam
being discharged from said first outlet passes, said condenser
adapted for removing water from said steam, and a heat exchanger
for heating a second portion of said steam being discharged from
said first outlet and being recycled to said material processing
chamber.
6. The apparatus of claim 5, further including a burner for heating
said first portion of said steam to an elevated temperature for
heating said second portion of said steam in said heat
exchanger.
7. The apparatus of claim 1, wherein said material supports
comprise a plurality of vertically stacked trays.
8. An apparatus for processing materials, the apparatus comprising:
a material processing chamber having an upper portion and a lower
portion, a rotatable assembly within said chamber extending from
the upper portion to the lower portion, said assembly including a
plurality of vertically displaced material supports supported on a
portion of said assembly; a drive device for causing the material
supports to rotate; a first inlet at the upper portion of the
material processing chamber adapted to receive material to be
processed and to deposit the material at least partially onto at
least one material support; a first exhaust outlet for exiting
exhaust steam generated within the material processing chamber; a
second inlet for recycling at least a portion of said exhaust steam
into the material processing chamber, and wherein said material
processing chamber is at least partially maintained under an inert
atmosphere by the recycled exhaust steam; and a heat exchanger
coupled between the first exhaust outlet and the second inlet for
heating at least a portion of said exhaust steam, at least a
portion of the heated exhaust steam recycled to the material
processing chamber.
9. The apparatus of claim 8, further comprising one or more fans
within the material processing chamber.
10. The apparatus of claim 8, further comprising a third inlet at
the lower portion of the material processing chamber for providing
a fluid to the chamber for quenching the material being processed
prior to discharge.
11. The apparatus of claim 8, further including a condenser for
condensing water or volatiles within said exhaust steam.
12. The apparatus of claim 11 further including a burner arranged
in fluid communication with said first exhaust outlet of said
material processing chamber for heating at least a portion of said
exhaust steam.
13. The apparatus of claim 8, wherein said heat exchanger is
operative for superheating said exhaust steam.
14. The apparatus of claim 8, wherein said material supports
comprise a plurality of vertically stacked trays.
15. A method for torrefaction of water-containing cellulosic
material within an inert atmosphere, said method comprising:
cascading cellulosic material between a plurality of rotatable
trays vertically stacked within a plurality of processing zones
provided within a material processing chamber, heating said
cellulosic material within said material processing chamber to
generate steam from the contained water in said cellulosic
material, discharging said steam generated from said cellulosic
material from said material processing chamber, and recycling at
least a portion of said steam to at least one of said processing
zones within said material processing chamber, wherein said steam
at least partially provides an inert atmosphere within said
material processing chamber.
16. The method of claim 15, wherein said material processing
chamber includes a discharge outlet for cellulosic material
processed within said plurality of processing zones, and a source
of fluid for cooling the processed cellulosic material being
discharged from said outlet.
17. The method of claim 15, further including a supply of inert gas
coupled to said material processing chamber for maintaining said
inert atmosphere.
18. The method of claim 15, further including heating said steam
prior to recycling to said material processing chamber.
19. The method of claim 18, wherein said heating comprises passing
at least a portion of said steam through a heat exchanger heated by
another portion of said steam discharged from said material
processing chamber.
20. The method of claim 15, further including condensing water or
volatiles from said steam discharged from said material processing
chamber.
21. A method for torrefaction of water-containing material within
an inert atmosphere, said method comprising: passing material to be
torrefied between a plurality of material supports within a
material processing chamber, heating said material within said
material processing chamber to generate steam from the contained
water within said material being processed, exhausting said steam
from said material processing chamber, heating said steam exhausted
from said material processing chamber, returning at least a portion
of the heated steam to said material processing chamber, wherein
said steam at least partially creates an inert atmosphere within
said material processing chamber, and discharging torrefied
material from said material processing chamber.
22. The method of claim 21, further including condensing at least a
portion of said steam prior to returning said steam after heating
to said material processing chamber.
23. The method of claim 21, wherein said material supports comprise
a plurality of vertically stacked trays
24. The method of claim 21, wherein said heating said steam
comprises superheating said steam.
25. The method of claim 21, further including supplying an inert
gas to said material processing chamber to maintain said inert
atmosphere.
26. The method of claim 21, further including quenching said
material being discharged from said material processing
chamber.
27. A method for processing material, comprising: feeding material
into a material processing chamber having an upper portion and a
lower portion, and a rotatable assembly extending between said
upper portion and said lower portion supporting a plurality of
vertically displaced material supports; applying heat within the
upper portion of said material processing chamber for drying said
material; collecting exhaust from said material processing chamber;
recycling the collected exhaust to said processing chamber;
torrefying said material within the lower portion of said material
processing chamber; and discharging said material from said
material processing chamber.
28. The method of claim 27, further comprising quenching the
torrefied material.
29. The method of claim 27, wherein the recycled exhaust at least
partially provides an inert atmosphere within said material
processing chamber.
30. The method of claim 27, further including heating said exhaust
before recycling to said material processing chamber.
31. The method of claim 30, further including using at least a
portion of said exhaust from said material processing chamber for
heating said exhaust to be recycled.
32. The method of claim 27, wherein said exhaust comprises
steam.
33. The method of claim 32, wherein said material comprises water
containing cellulosic material.
34. The method of claim 27, further including supplying an inert
gas to said material processing chamber.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of the filing date of
U.S. Provisional Application No. 61/195,092, filed Oct. 3, 2008,
the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] Torrefaction is generally known as the process of thermal
treatment of various cellulosic materials under an inert (i.e.,
non-oxidizing) atmosphere to convert such materials into a more
useful product. For example, wood when dried and heated to a
temperature of about 200.degree. C. to 290.degree. C. becomes what
has been referred to as "torrefied wood", i.e., a carbon-neutral
product with a high fixed carbon content, a high caloric value, a
very low moisture content, and which is generally non-hygroscopic
and rot proof, having retained practically all the pyroligneous
compounds. Examples of torrefaction and equipment therefore are
disclosed in U.S. Pat. No. 4,787,917 and U.S. Patent Application
Pub. No. 2003/0221363, the disclosures of which are incorporated
herein by reference.
[0003] The present invention relates in general to improvements in
systems and methods for drying and torrefaction of various
materials.
SUMMARY OF THE INVENTION
[0004] It has been known to first dry the material to be torrefied
in one piece of equipment, and to subsequently conduct the
torrefaction in a separate piece of equipment at higher
temperatures. This has obvious disadvantages. One aspect of the
present invention is to provide a single apparatus for both drying
and torrefaction of various materials in a torrefaction chamber,
particularly cellulose based materials such as wood and the like.
To this end, one aspect of the invention provides a stacked
multi-level tray heating apparatus having an upper portion or
section where the material to be torrefied is first dried. As the
material is dried, the moisture content driven off from the
material is converted into steam and/or gas, at least some of which
may be recycled into a lower portion or section of the apparatus
where the material is to be torrefied. According to another aspect,
the material may be subjected to quenching prior to discharge from
the apparatus.
[0005] By way of one example, raw wood is run through a wood
chipper to produce wood chips having a preferred particle size of
less than about %-inch. The wood chips may also include pellets,
shreds, sawdust, wood flours and the like. The chipped wood is
stored in a large hopper and is metered from the hopper into the
top of the drying chamber. No special treatment of the wood is
required prior to its introduction into the drying chamber. The
temperature of the feed stock entering the drying chamber depends
upon prevailing climatic conditions at the time of use, and can be
anywhere from about (-)10.degree. C. to about 40.degree. C.
Moisture content of the feedstock can be generally anywhere in the
range of about 10% to about 60% of the original weight of the
feedstock. However, it is contemplated that higher moisture
contents can be processed as well.
[0006] The feedstock is introduced into the top of the drying zone
at a uniform rate via a feeder where it is deposited onto the
uppermost tray in the torrefaction chamber. The uppermost tray of
the torrefaction chamber rotates slowly in a horizontal plane.
After being carried almost completely around on the tray, the wood
chips encounter a wiper bar which plows the woods chips until they
fall through one of several slots in the tray. The chips that have
been pushed off the first tray are now deposited onto a second tray
below the first tray. This tray is also slowly rotating in
synchronization with all of the other trays in the torrefaction
chamber. After continuing to rotate a short radial distance, the
chipped wood on the second tray may encounter a leveler bar if
provided which causes the pile of wood chips to be evenly
distributed upon the tray at a predetermined height. This
predetermined height is adjustable by way of example between about
1/2'' to about 3-inches. Distributing the pile of chips at a
uniform height allows all of the chips to be uniformly warmed by
the hot gas circulating within the top of the torrefaction chamber,
and this in turn results in a very uniform processing
condition.
[0007] The top section or zone of the torrefaction chamber is
temperature controlled to within about 1.degree. C. The exact
temperature used with the top zone depends upon the species of wood
being torrefied, the initial moisture content of the wood, and
other variables related to the properties of the feedstock.
[0008] After being carried almost completely around on the tray,
the wood chips encounter a wiper bar which plows the woods chips
until they fall through one of several slots in the tray. The chips
are then deposited upon the third tray down from the top. This
process continues until the torrefied chips are deposited upon the
lowermost tray. After being carried almost completely around on
this tray, the wood chips encounter a wiper bar which plows the
woods chips until they fall through one of several slots in the
tray onto the floor of the torrefaction chamber or directly to a
discharge chute. A final series of wipers push the torrefied chip
out the bottom discharge of the torrefaction chamber.
[0009] The torrefaction chamber is multi-zoned to give very
accurate drying and torrefaction of the wood chips as they progress
down through the torrefaction chamber. The present invention has
advantages of not forming a pyrochar. A pyrochared material has a
high ash content, and is less valuable because it is not as
hydrophobic, and will not pelletize as well as torrified wood. One
or more internal fans which can be mounted vertically in the center
of the torrefaction chamber pushes the inert heated atmosphere
around in a circular, horizontal pattern within the torrefaction
chamber and across the pile of chips as they lay on the rotating
trays.
[0010] In torrefaction, various gases are evolved, such as carbon
monoxide, carbon dioxide, various organic compounds, water, and
possibly other non-organic compounds. One aspect of this invention
is to burn the carbon monoxide and organic vapors and use the heat
evolved to provide some of the heat for drying and torrefying. The
inert atmosphere may consist substantially of steam and/or other
inert gas such as nitrogen. Torrefacation of the cellulosic
products, and more specifically the removal of bound water and
volatiles in the feedstock, are conducted in a closed, inert,
system which allows capture of volatile materials so that the
commercial value of the captured volatiles can be realized either
by combustion to recover their caloric value or by recovery as a
saleable by-product.
[0011] In accordance with one embodiment there is described an
apparatus for the torrefaction of water containing cellulosic
material within an inert atmosphere, the apparatus comprising a
material processing chamber having a plurality of processing zones
adapted for processing water containing cellulosic material, a
plurality of material supports within the processing zones for
receiving cellulosic material cascading within the chamber, the
material processing chamber having a first outlet for the discharge
of steam generated from processing the cellulosic material within
the processing zones, and at least one inlet for recycling at least
a portion of the steam into the material processing chamber,
whereby the steam at least partially provides an inert atmosphere
within the material processing chamber.
[0012] In accordance with another embodiment there is described an
apparatus for processing materials, the apparatus comprising a
material processing chamber having an upper portion and a lower
portion, a rotatable assembly within the chamber extending from the
upper portion to the lower portion, the assembly including a
plurality of vertically displaced material supports supported on a
portion of the assembly; a drive device for causing the material
supports to rotate; a first inlet at the upper portion of the
material processing chamber adapted to receive material to be
processed and to deposit the material at least partially onto at
least one material support; a first exhaust outlet for exiting
exhaust steam generated within the material processing chamber; a
second inlet for recycling at least a portion of the exhaust steam
into the material processing chamber; and wherein said material
processing chamber is at least partially maintained under an insert
atmosphere by the recycled exhaust steam; and a heat exchanger
coupled between the first exhaust outlet and the second inlet for
heating the at least a portion of the exhaust steam, at least a
portion of the heated exhaust steam recycled to the material
processing chamber.
[0013] In accordance with another embodiment there is described a
method for torrefaction of water-containing cellulosic material
within an inert atmosphere, the method comprising cascading
cellulosic material between a plurality of rotatable trays
vertically stacked within a plurality of processing zones provided
within a material processing chamber, heating the cellulosic
material within the material processing chamber to generate steam
from the contained water in the cellulosic material, discharging
the steam generated from the cellulosic material from the material
processing chamber, and recycling at least a portion of the steam
to at least one of the processing zones within the material
processing chamber, wherein the steam at least partially provides
an inert atmosphere within the material processing chamber.
[0014] In accordance with another embodiment there is described a
method for torrefaction of water-containing material within an
insert atmosphere, the method comprising passing material to be
torrefied between a plurality of material supports within a
material processing chamber, heating the material within the
material processing chamber to generate steam from the contained
water within the material being processed, exhausting the steam
from the material processing chamber, heating the steam exhausted
from said material processing chamber, returning at least a portion
of the heated steam to the material processing chamber, wherein the
steam at least partially creates an inert atmosphere within the
material processing chamber, and discharging the torrefied material
from the material processing chamber.
[0015] In accordance with another embodiment there is described a
method for processing material, comprising feeding material into a
material processing chamber having an upper portion and a lower
portion, and a rotatable assembly extending between the upper
portion and the lower portion supporting a plurality of vertically
displaced material supports; applying heat within the upper portion
of the material processing chamber for drying the material;
collecting exhaust from the material processing chamber; recycling
the collected exhaust to the processing chamber; torrefying the
material within the lower portion of the material processing
chamber; and discharging the material from the material processing
chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The subject matter regarded as the invention is particularly
pointed out and distinctly claimed in the concluding portion of the
specification. The invention, however, both as to organization and
method of operation, together with features, objects, and
advantages thereof may best be understood by reference to the
following detailed description when read with the accompanying
drawings in which:
[0017] FIG. 1 is front elevational view of an apparatus for
torrefaction of materials such as wood containing cellulosic
materials in accordance with one embodiment of the present
invention;
[0018] FIG. 2 is a cross-sectional view of another embodiment of a
torrefaction apparatus in accordance with the present
invention;
[0019] FIG. 3A is a top plan view of another embodiment of a
torrefaction apparatus in accordance with the present
invention;
[0020] FIG. 3B is a front elevational view of the torrefaction
apparatus illustrated in FIG. 3A;
[0021] FIG. 4 is a cross-sectional view of another embodiment of a
torrefaction apparatus in accordance with the present
invention;
[0022] FIG. 5 is a schematic illustration of a torrefaction
apparatus which may be implemented in accordance with the present
invention.
DETAILED DESCRIPTION
[0023] In describing the preferred embodiments of the invention
illustrated in the drawings, specific terminology will be used for
the sake of clarity. However, the invention is not intended to be
limited to the specific terms so selected, and it is to be
understood that each specific term includes all technical
equivalents that operate in a similar manner to accomplish a
similar purpose.
[0024] FIG. 1 shows an example of an apparatus 100 for drying and
torrefying material in accordance with one embodiment of the
present invention. As shown, a hollow chamber 110 forming the
torrefaction chamber is cylindrically or polygonally enclosed by
sidewall 116 which extends around the circumference of the chamber,
a top plate 112, and a bottom plate 114. The chamber has two
sections or portions--an upper portion 80 and a lower portion 85.
Each section will typically have multiple zones. The upper and
lower portions are contiguous with each other thereby forming
essentially a single continuous processing chamber where drying and
torrefaction take place simultaneously on a plurality of levels or
zones.
[0025] According to this aspect of the invention, drying of the
material is generally performed in the upper portion 80 and
torrefaction is performed in the lower portion 85. In this manner,
the apparatus can operate continuously by continuously supplying
material to be processed in the upper portion and removing
continuously the torrefied material from the lower portion.
Moreover, the drying process and torrefaction process may
complement one another and in some circumstances the torrefaction
process may compensate for inadequate drying. For example, if
material passing through the drying process is not sufficiently
dried, the torrefying process will compensate by causing the
moisture content of the material to evaporate. In this regard, the
upper portion 80 and lower portion 85 may operate at substantially
the same temperature, or one portion may operate at a higher or
lower temperature relative to the other portion.
[0026] The apparatus 10 may include any of a variety of components
for transferring the material through the different levels. For
example, the apparatus may incorporate a plurality of vertically
displaced material supports such as shelves, or trays 120.
According to one embodiment, the trays may include apertures,
thereby allowing material to pass through from one tray to a lower
tray. For example, the trays may be attached to a rotating
structure, and thus may rotate about a substantially vertical axis
as the structure rotates, with a cantilevered device extending over
the trays pushing material through the aperture. Alternatively, the
trays may remain stationary, and the cantilevered device may sweep
across the trays to transition the material thereon. Accordingly,
the material may be transferred from a feed port 10 onto a first
tray level, and continuously through the upper portion 80 and the
lower portion 85 via the tray levels to a discharge port 70. For
example, wiperarms may be used to transfer the material from one
tray level to the next tray level below, or gyrating trays with
large perforations may be used to shake the material from one tray
level down to the next tray. According to the invention shown in
FIG. 1, a plurality of spaced apart stacked trays 120 are rotated
by a shaft 130. As will be explained in further detail below with
respect to FIG. 2, the trays 120 may include apertures for
transferring the material from one tray level 120 down to the next
tray level as they rotate while processing the material.
[0027] Material fed through the port 10 for processing may be
undried or substantially undried, that is, having different levels
of moisture content. Typically, the feed material is wood or
another cellulosic material, such as bagasse, peat, grasses, peanut
shells, etc. having various water content (e.g., between about 10%
and 60% water), but may also include other volatiles to be
evaporated in the drying process. Cellulosic material contains
lignin, which maintains the caloric value of the torrefied end
product, and allows pelletization of the torrefied cellulosic
material. It is contemplated that non lignin containing materials
such as mosses can also be torrefied using the apparatus and
methods of the invention.
[0028] As the material is dried in the upper portion 80 of the
chamber, the moisture content from the material is evaporated
creating water vapor (steam). The steam rising through the chamber
10 may be discharged through the exhaust port 20 attached to the
top plate 112. At least some of this exhaust steam may be recycled
back to the chamber 110 to provide all or part of an inert
atmosphere. For example, the exhaust port 20 may be connected to a
heat exchanger 30, where the steam can be reheated to a superheated
state. The heat exchanger may be further connected to inlets 40 and
50, for recycling the heated steam to the upper portion 80 and/or
lower portion 85 of the chamber, respectively, at adjustable
ratios.
[0029] The torrefied material will catch fire if it is exposed to
the outside atmosphere before it is sufficiently cooled.
Accordingly, another aspect of the invention provides an inlet 60
for delivering a quenching substance to the lower portion 85 of the
chamber for quenching the torrefied material prior to discharge.
The quenching substance may be water, or any other inert liquid or
slurry. Quenching with water is the fastest way to do this cooling.
The quenching substance may be discharged with the torrefied
material through discharge port 70, or may be discharged separately
through another outlet (not shown), thereby enabling a constant
flow of the quenching substance to the chamber. The quenching
substance may be recycled to the chamber, and cooled through a
refrigeration device (not shown) as may be desired.
[0030] FIG. 2 shows an example of an apparatus 100 for processing
materials according to another embodiment of the present invention.
Certain aspects of the construction of the apparatus to be
described is disclosed and described in co-pending application Ser.
No. 11/975,144, filed on Oct. 17, 2007, the disclosure of which is
incorporated herein by reference. The apparatus 100 has particular
application where toxic or reactive gasses may be present or are
generated within the apparatus during torrefaction of the material.
The apparatus 100 includes a chamber 110, in this instance a
drying/torrefying chamber, wherein the materials are processed. The
apparatus 100 further includes at least one drive assembly 160,
which may power operations within the chamber 110, though being
located outside.
[0031] The drying/torrefying chamber is cylindrically enclosed by
sidewall 116 which extends around the circumference of the chamber
110, a top plate 112, and a bottom plate 114. The chamber 110 is
supported on a base 174 by supports 170 and may be connected via
expansion joints 172. The expansion joints 172 enable the supports
170 to move as the chamber expands due to, for example, increased
heat therein. This reduces stress applied to the structure of the
apparatus 100.
[0032] Inside the chamber 110, the apparatus may incorporate a set
of trays 120 surrounding a set of vertically-aligned fans on a fan
shaft 130. The fans may circulate the atmosphere inside the chamber
over the material in the trays 120. The material to be processed
may be placed on the top tray level and progressively transferred
to lower tray levels. Each tray is connected to at least one
stanchion 126, wherein several stanchions are positioned around a
fan shaft 130, thereby forming a squirrel cage. Coupled to the
stanchions 126 is a turntable 182 at the lower end of the chamber.
According to one embodiment, the turntable 182 is connected to a
rotating tray structure which surrounds the fan shaft 130. Drive
gears 160 cause the turntable 182 to rotate, thereby causing the
stanchions 126 and trays 120 to revolve.
[0033] A tray wiper 122 in the nature of a cantilevered device may
be positioned above each tray 120. As each tray 120 rotates, the
tray wiper 122 transfers the material to the next tray level. A
rigidly mounted leveler 125 may brush across the top of the
material placed thereon, thereby leveling the material and exposing
materials underneath the top portion to the environment within the
chamber 110. Material that is spilled by the tray wiper 122 over
the side of the tray (i.e., between the shaft and the rotating
trays) falls onto catch plate 124. This plate 124, angularly
positioned with respect to the trays 120, causes the material which
is spilled off a tray 120 above to fall into a tray 120 below. In
this manner, the material being processed cascades downwardly from
the upper tray to the lower tray.
[0034] According to one aspect, a turntable sweeper 180 may be
positioned above the turntable 182. The turntable sweeper 180 may
prevent complications potentially caused by materials falling onto
the turntable 182.
[0035] As the processed material is being rotated and moved as
described above, further drying elements may be implemented within
the chamber 110. For example, several fans 140 may be included in
the chamber 110 to facilitate circulation of heated gasses and
superheated steam therein and to effect a more even temperature
profile within the chamber. The fans 140 may be connected to the
fan shaft 130 by keys 146. The fan shaft 130 may extend beyond the
bearing assembly 250 and connect to a reducer 190 at its lower end.
The reducer 190 may be powered electrically, or by other sources
such as hydraulic, steam, gas, or a mechanical crank. As the
reducer 190 causes the shaft 130 to rotate, fan blades 140 would in
turn rotate, thus pushing the internal environment within the
chamber across the trays 120.
[0036] The processed material may further be exposed within the
chamber 110 to gasses provided through an inlet 152. For example, a
duct may be connected to the inlet 152, and regenerated superheated
steam, heated gasses, desiccants, or other inert, reactive, or
non-reactive gasses may be provided to the upper portion of the
chamber 110 through the duct. Similarly, a duct may be connected to
inlet 154, and regenerated superheated steam, heated air, gasses,
desiccants, or other inert, reactive, or non-reactive gasses may be
provided to the lower portion of the chamber 110 through the duct.
An exhaust 150 provides an outlet for the gasses which may be
recycled to the chamber 110 through the inlets 152, 154. According
to one embodiment, ducts connected to the exhaust may lead to a
conditioning unit such as a heat exchanger 30 further connected to
the inlets 152, 154, thereby allowing the gasses to be recycled
through the chamber 110.
[0037] Alternatively or additionally, internal heating within the
chamber may be used. For example, in smaller units electrical
heaters may be placed within the chamber to heat the atmosphere. In
other units, U-tubes (i.e., hollow tubes with flames inside) may be
positioned within the chamber and connected to an exhaust and a
natural gas inlet port. As the water content from the processed
materials evaporates, the fans may blow the steam across the
U-tubes for reheating.
[0038] To prevent the gasses provided to the chamber 110 from
escaping, seal assemblies are placed around the shaft 132 and near
the opening 118. Shaft 130 may be formed of metal or any variety of
other materials. Further, although the apparatus 100 as described
herein includes a rotating shaft 130, the shaft 130 may be capable
of other motions, such as gyrating.
[0039] Referring to the remaining figures, there is illustrated an
apparatus 200 in accordance with another embodiment of the present
invention. By way of brief description, FIG. 3A is a top plan view
of a drying/torrefying apparatus, and FIG. 3B is a front view
thereof. FIG. 4 is a detailed view of the inner components of the
drying/torrefying apparatus. FIG. 5 is a diagrammatic view of the
valves and connections providing fluid or gaseous substances to and
from the chamber of the drying/torrefying apparatus and elsewhere
in the system, such as the burner.
[0040] Substantially undried cellulosic material is dried and
torrefied in the dryer/torrefier apparatus which is constructed as
one piece of equipment. The moisture evaporated from the wood
during drying and torrefying is used as an inert medium in the
lower portion 204 of the apparatus where the wood is being
torrefied. The water vapor may be heated to a superheated state
internally within the apparatus and/or circulated via duct 220
through an external heat exchanger 218 before being recycled back
into the apparatus. The inert super-heated steam may be
supplemented by another inert gas such as nitrogen. If the
torrefied material gets exposed to oxygen, e.g. from air, before it
is sufficiently cool upon discharge from the apparatus, it will
ignite, which would destroy its beneficial characteristics and be a
safety hazard.
[0041] This system of drying and torrefaction in a single apparatus
is more thermally efficient than drying the material separately. It
is also simpler and less expensive from the view point of capital
expenditure and operating costs. According to one aspect, such
drying and torrefaction may be performed in a TurboDryer.RTM. unit
sold by WYSSMONT.RTM. Corp. as may be modified pursuant to the
present invention. However, other systems which may be used include
any type of a vertical apparatus with trays or plates or hearths
that retain the material and in which the material moves down
through the apparatus by means of arms, blades, or other such
devices.
[0042] The apparatus may also incorporate a quenching section. For
example, water can be provided at the bottom of the apparatus or in
the discharge area for the processed material. According to one
aspect, water may be provided in a constant flow to ensure that the
water remains under a predetermined temperature. For example, an
additional inlet may be fed to a lower portion of the apparatus,
with an additional outlet being placed in the lower portion as
well. The inlet and outlet may be positioned on substantially
opposing sides of the internal processing chamber 206 provided in
the apparatus, or the outlet may be the same as the discharge for
the processed materials. In this regard, cool water may be fed to
the chamber through the inlet, and discharged through the outlet,
thereby creating a steady flow of cool water. Moreover, the
discharged water may be cooled in a separate unit, and recycled
back to the inlet. The quenching is to cool off the torrefied
material quickly. If the torrefied material gets exposed to oxygen,
e.g. from air, before it is sufficiently cool it will ignite which,
would destroy its beneficial characteristics and be a safety
hazard. An application in which the product is not quenched may be
cooled under inert gas to avoid having the hot torrefied material
start combusting.
[0043] Torrefied product can be discharged through a double airlock
with intermediate purge to prevent exposure to oxygen before the
product is reduced in temperature to below the auto-ignition
temperature of the torrified cellulosic material.
[0044] A system is shown in FIGS. 3-5 where a portion of the
exhaust 210 from the torrefaction, which has a number of different
types of exhaust gases and vapors including but not necessarily
limited to carbon monoxide, carbon dioxide, nitrogen, water vapor,
acetic acid and/or other organic vapors, is circulated to a
condenser 214 having an inlet 215 and an outlet 217 which removes
the water and other condensibles. The exhaust gasses could also be
discharged directly to the atmosphere if environmentally permitted,
or passed through a thermal oxidizer. From the condenser 214, the
remaining exhaust gases may be provided to a burner 212, where it
is burned with a supplementary heating system. That is, because the
excess air in the burner 212 would cause problems (i.e., fire) in
the drying/torrefying chamber, the exhaust gases are passed through
an air-to-air heat exchanger 218 for heating the remaining portion
of the discharged steam from duct 223 to be recycled. Steam
generated generally within the upper drying section of the
torrefaction chamber is exhausted via conduit 210 via a circulation
fan 221. The portion of the exhausted steam to be recycled is fed
to heat exchanger 218 where it is reheated, e.g., superheated, via
the heated gases supplied from burner 212. The superheated steam
from the heat exchanger 218 is fed to multiple sections or zones of
the torrefaction chamber to provide heat for drying and
torrefaction through one or more inlet ducts. In addition, the
superheated steam also provides the inert atmosphere within the
torrefaction chamber.
[0045] A process for drying/torrefying wood as an example will now
be described with respect to the apparatus described above. Wood is
one type of cellulosic material. Wood is a generic name for a wide
range of differing materials. Generally, wood is divided into two
major classes: hardwoods or softwoods.
The following table gives relative compositions:
TABLE-US-00001 Component % mass in softwood % mass in hardwood
Cellulose 40 to 44% 43 to 47% Hemicellulose 25 to 29% 25 to 35%
Lignin 25 to 31% 16 to 24% Extractives 1 to 5% 2 to 8%
[0046] When torrefying at elevated temperature, the hemicellulose
portion of the wood will begin to decompose at lower temperatures
than the other components of wood. This decomposition occurs
rapidly in the presence of oxygen and less rapidly when oxygen is
not present.
[0047] The apparatus and method of the present invention provides
exact temperature control in each drying/torrefaction zone which
maximizes the temperature at which torrefaction can occur, without
crossing over into the temperature at which the exothermic reaction
of the hemicellulose occurs. The higher the temperature that can be
achieved while torrefying, without causing a decomposition of the
hemicellulose, produces a more commercially valuable torrefied
wood. Torrefied wood is sold based upon its net caloric value. In
operation, the preferred temperatures in the torrefaction chamber
is in the range of about 220.degree. C. to about 280.degree. C.,
and more preferably from about 260.degree. C. to about 280.degree.
C., although temperatures in the range of about 200.degree. C. to
about 300.degree. C. are contemplated.
[0048] In implementing the torrefaction process using a rotating
tray type apparatus having a plurality of stacked trays 222 with
internal circulation fans 224 on a single shaft 226 (such as
describe above), the material being processed drops down through
the stationary feed chute 228 onto the top tray of the rotating
trays. Ideally, the material falls onto the trays uniformly. The
material may be spread out using, for example, a mounted leveler
230 to give more uniform drying of the material on the trays by
exposing materials underneath the top portion to the environment
within the chamber. The material on the trays rotates most of the
way around the interior of the chamber forming the drying
section.
[0049] A tray wiper 232 in the nature of a cantilevered device may
be positioned above each tray level 222. As each tray 222 rotates,
the tray wiper 232 transfers the material to the next underlying
tray. The material that is spilled by the tray wiper may fall onto
a catch plate 124 such as shown in FIG. 2 or other suitable device.
The plate 124, angularly positioned with respect to the trays 222,
causes the material which is spilled off a tray above to fall onto
a tray below. In this manner, the material being processed cascades
downwardly from the top trays to the bottom trays. This action is
repeated throughout the drying section (the upper portion 80) of
the dryer/torrefier apparatus.
[0050] In the upper drying section in the preferred operation, the
water that is evaporating from the processed material is retained
in this section where it acts as an inert medium to prevent the
wood from burning at temperatures in which it would normally
combust in air. The atmosphere with the evaporated water may also
be removed from the apparatus via conduit 210 and then recycled
back into the lower torrefaction section of the apparatus after
being re-heated via burner 218 as described above. It is also
contemplated that the water vapor can be recycled back into the
upper drying section 80 if desired.
[0051] Initially the inert atmosphere can be composed of 100%
nitrogen or some other inert gas including steam. As steam evolves
from the wood chips being torrefied, the inert atmosphere is
partially or wholly displaced by evolved water which eventually
becomes a superheated steam. Since 100% nitrogen atmosphere may be
initially used during the initial startup, for all practical
purpose the torrefaction chamber runs all of the time with
superheated steam, a small amount of nitrogen, and some volatiles
creating the inert atmosphere. The torrefaction chamber can
optionally include a nitrogen flooding system which will flood the
torrefaction chamber with nitrogen in the event of a high oxygen
content developing within the torrefaction chamber due to an upset
condition. This is a safety control designed to prevent fires
within the torrefaction chamber.
[0052] The purpose of the rotating internal fans 224 as previously
described is twofold. The fans immediately mix the incoming hot
steam with the steam currently within the torrefaction chamber. For
example, steam which has been externally heated to a temperature as
high as 300.degree. C. can be introduced into the torrefaction
chamber at any of several points along the vertical height of the
torrefaction chamber in any combination. The volume of superheated
steam introduced into the torrefaction chamber at each entry point
can be separately controlled to optimize the process.
[0053] The superheated steam which is introduced into the
torrefaction chamber is immediately mixed with steam already within
the torrefaction chamber which may be and is usually at a much
lower temperature. At the top of the torrefaction chamber the
incoming feedstock temperature could be 10.degree. C. As it begins
to dry, the water trapped within the wood is evolved. This water
vapor immediately mixes with the steam at 300.degree. C. to yield a
much lower internal drying temperature in this zone of the
torrefaction chamber. The exact temperature within the uppermost
zone of the torrefaction chamber is monitored and controlled. Both
the inlet temperature and/or the inlet flow can be controlled to
yield any zone temperature required for optimization of the
process.
[0054] The size of the top zone can be controlled by design of the
central fans 224 or by installation of baffle plates to separate
higher trays from trays lower down in the construction of the
torrefaction chamber. The uppermost zone can consist of any number
of trays, but in one example, is in the range of three to fifteen
trays. The top zone is typically controlled at a temperature in the
range of about 200.degree. C. to about 260.degree. C. range.
[0055] As the wood chips continue down through the torrefaction
chamber, the chip temperature continues to increase. The hotter the
steam used to dry the chips the more rapid the increase in chip
temperature. As the chips continue downward through the
torrefaction chamber, they may encounter higher steam temperatures
as they pass into the next torrefaction chamber zone. This process
continues through successively hotter zones until the chips are
reduced in water content to about 1% to about 3%. At this point the
chips begin to torrify. Volatiles are driven off and additional
water is removed from the wood chips. During the downward passage
of wood chips through the torrefaction chamber as few as one
temperature zone or multiple zones (e.g., eight or more temperature
zones) may be encountered depending upon the design of the
torrefaction chamber.
[0056] The wood chips evolving their water content results in the
partial displacement of the nitrogen initially within the
torrefaction chamber during startup. Once operating, generally
without stoppage for weeks or months at a time, there remains no
significant amount of nitrogen within the torrefaction chamber. The
internal, inert atmosphere is composed of water in the form of
superheated steam, residual nitrogen, and volatiles that have been
evolved from the wood chips. It is contemplated that supplemental
inert gas can be added to the torrefaction chamber to maintain an
inert atmosphere.
[0057] This water vapor is discharged as superheated steam from the
torrefaction chamber at one or more points along the vertical sides
of the chamber, the top of the chamber via conduit 210, or the
bottom of the chamber. The superheated steam can be condensed via a
condenser 214 to remove a portion of the water and/or other
volatiles from the system. For example, if the wood chips are
evolving water at the rate of 20,000 pounds per hour of water, the
condenser can be designed to remove the 20,000 pound per hour from
the system once stabilization of the inert atmosphere has
occurred.
[0058] In accordance with one embodiment of the invention, the
condenser 214 has two inlets and two outlets. One inlet is for that
portion of the superheated vapor exiting the torrefaction chamber
in duct 222. The second inlet is for the cold water used to cool
the superheated steam and to condense out the excess water. One
outlet is for the residual superheated vapor which is now colder,
no longer superheated, and carrying less remaining water. The
second outlet from the condenser is for the cooling water which is
now warmer due to having been used to cool the superheated steam.
The remaining exiting residual vapor via duct 223 is re-heated via
heat exchanger 218 using heated exhaust from burner 212 to an
elevated temperature and then injected back into the torrefaction
chamber at any number of zones where it once again can be used to
heat the wood chips and to capture evolved water from the wood
chips. The superheated steam provides the inert atmosphere within
the torrefaction chamber. The amount of the superheated vapor being
supplied to the condenser 214 versus the amount of the superheated
vapor being supplied to the burner 218 to be recycled can be
controlled as may be required by the water content and the
water-handling capacity of the burner.
[0059] By drying and torrefaction in one piece of equipment, higher
temperatures can be used in the drying section to reduce the drying
time. In the lower torrefying section 85, temperatures between, for
example, in the range of about 200.degree. C. to about 290.degree.
C. can be used. One advantage of drying and torrefying in the same
unit is that you do not have to control the final moisture content
from the drying section very closely as you would with separate
systems. In the rotating tray type apparatus, the temperature and
velocities of the heating medium are easily adjusted.
[0060] In an apparatus where quenching occurs inside the unit, the
entire bottom of the torrefaction chamber (as part of it) can be
filled with water which is continuously replenished. The hot
torrefied cellulose material is wiped off the bottom shelf into the
water to prevent it from catching fire after it leaves the
apparatus. The hot torrefied material must be cooled to a
temperature where it will not combust in contact with air,
otherwise it can burst into flames. Quenching can also be done in
the discharge chute of the torrefaction chamber or in other
equipment that follows the torrefaction chamber.
[0061] One advantage of the system is that drying and torrefaction
are done essentially under atmospheric pressure. Another advantage
is that carbon monoxide is maintained in the system rather than
outside as could occur with other drying and torrefaction
systems.
[0062] The design of the torrefaction chamber allows several
variables to be controlled: 1) The exit points from which the
superheated steam leaves the torrefaction chamber can be designed
to occur at one or more elevations simultaneously; 2) The amount of
superheated steam removed from the torrefaction chamber at each
exit point can be controlled; 3) The amount of water removed from
the superheated steam can be controlled; 4) The re-injection
temperature of the superheated steam and the location of the
re-entry points along the surfaces of the torrefaction chamber can
be controlled individually; 5) As the product progresses further
down through the torrefaction chamber the superheated steam begins
to include more and more volatile gases; and 6) Superheated vapor
containing volatiles can be removed from one or more locations
along the vertical side of the dryer. As before, the superheated
vapor can be treated to remove excess water and/or volatile
components.
[0063] In the lower sections of the torrefaction chamber there is
very little excess steam present since the wood chips are no longer
giving up excess water. The unique zone design of the torrefaction
chamber allows the collection of volatile components to occur most
efficiently in the lower sections without the need to remove large
amounts of water from the volatiles. The torrefaction chamber
system may include numerous discharge points from which superheated
steam can be exited and then treated to remove water vapor and/or
volatiles. The chamber may also include numerous re-entry points
into which superheated steam can be re-injected into the
torrefaction chamber at controlled temperatures. By combining both
the drying process and the torrefaction process in a single
vertical design, the torrefaction process can be designed to
produce a torrefied wood product having maximum caloric value and
commercial value. The ability to precisely control both the drying
conditions and the torrefaction conditions provides the advantage
whereby the lignin present in the cellulosic material is neither
broken down nor driven off.
[0064] The torrefaction chamber as thus far disclosed can be zoned
into multiple drying/torrefaction zones. This can be done by
physically dividing the horizontal cross section into compartments
using horizontally mounted baffle(s) or by design of the fans so
that temperature zones are created by the segmented nature of the
fan design. It is contemplated that one can use a combination of
these two methods.
[0065] Drying conditions are controlled by regulating the
temperature of each drying/torrefaction zone. There are several
possible ways of doing this. One contemplated example includes the
total caloric input into the system is determined by the external
burner firing rate. Heat recovery devices such as condensers and
air pre-heaters are used to recover "waste" heat and to reduce the
energy input into the system. In another example, individual zones
are created and controlled by: regulating the volume of steam
introduced into each zone; by regulating the temperature of the
steam introduced into each zone; by regulating the vertical height
of each zone; by regulating the vapor takeoff from each zone; by
regulating the temperature at which the steam is condensed; by
regulating the temperature at which the volatiles are condensed;
and by any combination of the foregoing.
[0066] By way of example, an input of approximately 1500 BTU's per
pound of wood is contemplated to produce a torrefied product having
a usable caloric value of approximately 10,000 BTU's per pound.
This ratio is impacted by the initial moisture content of the
cellulosic material and by the species of cellulosic material being
torrefied.
[0067] Pelletization of the torrefied wood allows the torrefied
wood to be used in commercial applications. Processes that produce
a product with less lignin result in pellets that are more
sensitive to breakage, create dust problems at the point of usage,
and have less commercial value. The lignin in the product produces
a strongly hydrophobic material. This is desirable because prior to
use as a fuel, the torrefied, pelletized, cellulosic material will
be stored in the open and is exposed to climatic conditions. The
more hydrophobic the torrefied, cellulosic, material the less
likely the pellets will absorb water in high humidity conditions,
or will absorb water during a rain or snow. Any water absorbed
reduces the commercial value of the torrified material by reducing
the net caloric value. The process produces an end product that is
more uniform compared with products produced by other processes.
The end product is both uniform, particle-to-particle, but also
throughout the cross-section of each particle. A uniform product
allows for precise and reproducible pelletizing of the torrified
cellulosic material.
[0068] Although the invention herein has been described with
reference to particular embodiments, it is to be understood that
these embodiments are merely illustrative of the principles and
applications of the present invention. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
invention as defined by the appended claims.
* * * * *